Sea Lion

Sea lions belong to Otariidae, the eared seals, a family of 15 living species in seven genera that are commonly known as sea lions or fur seals. They are semiaquatic, feeding and migrating in the water but breeding and resting on land or ice. They live in subpolar, temperate and equatorial waters of the Pacific and Southern Oceans and the southern Indian and Atlantic Oceans, and are absent from the north Atlantic. Small external ear flaps set them apart from true seals, and they can turn their hind limbs forward to walk on all fours. Carnivorous, they feed on fish, squid and krill, with sea lions tending to feed closer to shore on larger fish.

About the sea lion

Sea lions are large, eared marine mammals that, together with the fur seals, make up the family Otariidae. They have external ear flaps, long front flippers, short thick hair and a big chest, and they can walk on all four flippers on land. Six living species range from subarctic to tropical seas in both hemispheres.

"Sea lion" is a group name rather than a single species. The six living species are the Steller sea lion, the Australian sea lion, the South American sea lion, the New Zealand sea lion, the California sea lion, and the Galápagos sea lion. A seventh, the Japanese sea lion, went extinct in the 1950s. They are spread across five genera, Eumetopias, Neophoca, Otaria, Phocarctos and Zalophus.

Sea lions are related to walruses and to seals. Compared with fur seals, sea lions have coarse, short fur instead of dense underfur, greater bulk, and they take larger prey. Genetic studies show the old split of the family into a sea lion subfamily and a fur seal subfamily doesn't hold up, since the northern fur seal is more closely related to some sea lions than to other fur seals. The traditional distinction is still useful for describing the animals, though.

Size varies by species and by sex. A male California sea lion averages about 300 kg (660 lb) and 2.4 m (8 ft), while a female averages about 100 kg (220 lb) and 1.8 m (6 ft). The largest are Steller sea lions, which can weigh 1,000 kg (2,200 lb) and grow to 3.0 m (10 ft). Within a species, animals tend to be smaller in the tropics and larger at higher latitudes, peaking in sub-polar regions. In cold water a bigger body has an advantage, because it has less surface area relative to its size.

Behavior and diet

Sea lions are fast, strong swimmers. They usually travel at about 30 km/h (18 mph) and can reach about 56 km/h (35 mph) at top speed. Their streamlined bodies reduce drag and give good propulsion, making their swimming energy efficient.

They are also built for diving. As a sea lion descends, rising water pressure collapses the air sacs in its lungs and pushes air into the stiffer airways, which limits nitrogen uptake and lowers the risk of decompression sickness. The heart slows well below its surface rate, a response called bradycardia, and digestion slows by at least 54 percent to save oxygen. Sea lions also tolerate stored carbon dioxide better than land mammals: after a long dive, carbon dioxide leaves the blood more slowly than oxygen is restored, but the raised level does not seem to affect their diving.

Sea lions eat a lot at once, about 5 to 8 percent of their body weight in a single feeding, or roughly 6.8 to 15.9 kg (15–35 lb). California sea lions feed mostly offshore in coastal upwelling areas, taking squid, anchovies, mackerel, rockfish and sardines. They will also take fish from fishing gear and at dams.

Breeding happens on land or ice at colonies called rookeries. In Steller sea lions, adult males set up territories in early May, and females arrive in late May. Males mature at 5 to 7 years but usually do not hold territories until 9 to 13 years old. Mating is polygynous: a successful male mates with many females, some males never mate, and males rarely help raise pups. Females usually give birth to a single pup.

Range and habitat

Sea lions range from subarctic to tropical waters in both the Northern and Southern Hemispheres. The one major gap is the northern Atlantic Ocean, where no sea lions live. Their ability to control blood flow to the skin and flippers, along with blubber and behavior such as hauling out onto land, lets them cope with both cold and warm climates.

Each species has its own region. California sea lions feed in coastal upwelling zones and crowd docks in places such as San Francisco Bay. Galápagos sea lions have been called "the unofficial welcoming committee of the Galápagos Islands." South American sea lions live along coasts such as Chile's and Uruguay's, Australian sea lions are found in Western Australia, and New Zealand sea lions, long confined to the subantarctic islands, are slowly returning to the mainland. New Zealand sea lions are the only pinnipeds that regularly move up to 2 km (1.2 mi) inland into forests.

Sea lion vs seal

Sea lions and true seals are both pinnipeds, but they belong to different families and move very differently.

The harbor seal is a familiar true seal for comparison. An animal with external ear flaps that walks on all four flippers is an eared seal, a sea lion or a fur seal, rather than a true seal.

Conservation status

Conservation status differs from species to species. Three species, the Australian, Galápagos and New Zealand sea lions, are listed as endangered, and the Japanese sea lion has been extinct since the 1950s.

Threats vary by region. Commercial fishing competes with sea lions for prey such as pollock. Climate change has increased toxic algae blooms, and toxins passed up through sardines and other fish can cause brain damage and epilepsy in sea lions. Parasites take a toll on pups. Eye flukes have heavy impacts on young Galápagos sea lions, an effect that global warming appears to compound, and hookworms affect Australian and New Zealand sea lion pups. Historic hunting cut numbers sharply; South American sea lions in Chile are now recovering, with about 165,000 animals, while New Zealand sea lions were wiped out on New Zealand's mainland for over 150 years before a female gave birth there in 1993.